1. Field of the Invention
The present invention is generally concerned with imaging devices of the type used by opticians to perform various position measurements on a person wearing an eyeglass frame for the purpose of fitting lenses to the frame.
Briefly, the aim is to acquire an image of the person wearing the eyeglass frame in order to measure the position of their pupils relative to the rims or surround of the frame.
2. Description of the Prior Art
The imaging devices used for this purpose include an image acquisition device equipped with a video camera to perform the required imaging and to which there therefore corresponds an imaging axis and a viewing screen enabling the practitioner to control the device and to which there therefore corresponds an observation axis.
The aim is to measure on a photographic or video image the position of the optical axis or vision axis of either or both eyes of the person concerned relative to the frame of reference consisting of the eyeglass frame to be fitted with lenses. It is therefore important to allow for the fact that the person's pupils are in a plane to the rear of the median plane of the eyeglass frame spaced from this latter plane by a certain distance, which is generally in the order or 12 mm, and that for looking horizontally the median plane of the eyeglass frame is usually inclined at an angle to the vertical, commonly referred to as the pentoscopic angle, and which generally varies in the range 5.degree. to 15.degree., with an average value in the order of 10.degree..
If these two parameters are not allowed for, the parallax error that can result can lead to a positioning error of a few millimeters between the optical axis of the lenses and the vision axis of the person, which is to the detriment of the latter's quality of vision.
A general aim of the present invention is an arrangement which overcomes this problem in a very simple and a very effective way and which also has other advantages.